Process for treatment of hydrocarbons



Oct. 9, 1962 F. F. A. BRACONIER ET AL 3,957,707

PROCESS F OR TREATMENT OF HYDROCARBONS Filed Feb. 2. 1959 2 SheetsSheet2 United States Patent Office 3,057,707 Fatented Oct. 9, 1962 PROCESS;FOR TREATMENT OF HYDROCARBUNS Frdric Francois Albert fsraeonier,Plainevaux, and dean Joseph Lambert Eugene Riga, Liege, Belgium,assignors to Socit Beige de lAzote et desProduits Chimiques du Marly,Liege, Belgium Fiied Feb. 2, 195 Ser. No. 790,568 9 Claims. (Cl. 48-496)This invention relates to a process and an apparatus for rapidlyextinguishing the furnaces for the partial combustion of hydrocarbons,used for the preparation of less saturated hydrocarbons such asacetylene and olefines, or synthesis gas consisting mainly of carbonmonoxide and hydrogen.

It is known that said furnaces for the partial combustion comprise, asessential parts, a chamber for mixing the reagents (gaseous or vaporizedhydrocarbon and oxygen), a partial combustion chamber communicating withthe preceding chamber, e.g., through a distributor or a grating fordistributing the gaseous mixture, and a device for quenching theresulting mixture to terminate the pyrolysis reactions.

It is also known to reduce the oxygen consumption by preheating thereagents at a high temperature, which is however lower than that whichwould produce a spontaneous ignition of the hydrocarbon in the mixingchamber. For preventing the flame formed in the combustion chamber frompropagating in the mixing chamber, the linear velocity of the gaseousreagents is kept higher than that of the flame propagation.

Even with proper design, however, there remains some danger due toaccidental causes, such as the variations of the throughput and thecomposition of the gaseous reagents, that backfiring may occur. In suchevent the hydrocarbon to be pyrolyzed takes fire in the mixing chamber.It is thus desirable to make provision for extinguishing such flame assoon as possible to avoid important loss or even a complete destructionof the distributor and the mixing chamber.

Numerous expedients have already been proposed or experimented with forthis purpose. However, they have failed due to the lack of sensitivityof the combustion detector in the mixing chamber and because of thearrangement taken for extinguishing the furnace. Most generally blowingnitrogen into said chamber and substituting nitrogen streams for thestreams of the gaseous reagents are not sufficiently rapid andefiicient.

The present invention overcomes these drawbacks and makes it possible toextinguish the furnace even in a fraction of a second, when apre-ignition occurs in the mixing chamber.

One process according to this invention utilizes an instantaneoustemperature detecting means to respond to pre-ignition in the mixingchamber. Such means may with advantage he a bare thermo-couple locatedin the bottom of said chamber, near the distributor. Said thermo-couplewhen heated by the pre-ignition gives an electric signal which is usedto trigger the starting up, auto matically and simultaneously, of thefollowing operations.

(1) Closing the conduits feeding the gaseous reagents by means of valvessituated on the cold portion of said conduits, i.e. upstream beyond thepreheaters for said reagents.

(2) Flooding with nitrogen the conduit which has been feeding thehydrocarbon to be pyrolysed.

(3) Blocking the oxygen in the preheating section by blowing nitrogeninto the oxygen conduit at a point as close as possible to the mixingchamber.

(4) Closing the product gas outlet conduit.

(5) Opening a venting device for venting gases from the pyrolysisfurnace.

(6) After a suflicient period for complete purging of the hydrocarbonfeeding section, nitrogen is then introduced in the oxygen feedingconduit, just downstream the closing valve of said conduit.

These six different operations for opening and closing the conduits arerealized by means of automatic valves driven simultaneously for thefirst five of these operations and With a slight delay for the lastoperation. The thermocouple in the case of a pre-ignition in the mixingchamber, transmits an impulse to a signal-responsive valve operatingdevice e.g., consisting of several electromagnetic relays with contacts,each valve being driven by an individual electromagnetic devicecontrolled by one of said relays, as hereinafter more specificallydescribed.

To secure the maximum safety of the process, closed circuits through therelay contacts are used, i.e. during the normal run of the furnace, allthe contacts are closed and only when a pre-ignition occurs in themixing chamher, the impulse transmitted by the detecting thermocouplecauses the opening of the contacts and the automatic working of thevalves controlled by the relays.

When using the inverse method, i.e., when the driving relays of thevalves are operating by closing the contacts (the latter being open at anormal run of the furnace), it is still to be feared that, due to theoxidation of the contacts, the closing of the latter may be hindered.

The invention herein disclosed is designed to avoid damage, in suchcases, by very rapid and fully efficient operation of said valves. Tothis end certain conditions are controlled as will be disclosedhereinafter, as applied to a partial combustion furnace schematicallyrepresented in the accompanying drawing showing such apparatus partly invertical section, partly in diagrammatic layout.

Said furnace, in the example shown, is of the type covered by ourcopending application Serial No. 726,248, filed April 3, 1958. As hereshown, the furnace comprises an annular feed-commingling zone 1, forcontacting and intimately mixing the gaseous reagents, said zone beingextended to an annular final mixing chamber 2 widening downwards andsurrounding a central hollow conical core 3, the apex of which is at thecenter of the distributor 4. The distributor 4 connects said mixingchamber 2 to the pyrolysis chamber 5 including the device 6 forquenching the product gases by transversely injecting cold water.

The conduit 7 connected to the oxygen supply is provided with anautomatic shut-off valve 8 and with a preheater 9. Conduit 7 projectsinto the hollow central core 3, as shown. The conduit 10 for introducingthe hydrocarbon to bepyrolyzed in the mixing device is also pro- Theconduit 13 for carrying off the cooled pyrolysisgas es to the acetylenepurification and concentration unit, is provided with an automaticshut-off valve 14 and a device 15 for venting the gases when said valveis closed.

The temperature-responsive device for detecting a spontaneous ignition,or back-firing, in the mixing chamber,

is shown diagrammatically as a bare thermo-couple 16, projecting severalcentimeters into the mixing chamber 2, near the distributor 4. Theconduits 17, 18 and 19, provided with automatic valves 20, 21 and 22respec.

tively, are used to blow in nitrogen under pressure for rapidlyextinguishing the furnace when any combustion.

occurs in the mixing chamber 2.

The bare thermo-couple is connected to a relay box 3 comprising eightopen electromagnetic relays, the magnetic winding circuits of which areenergized (after amplification) by the thermo-couple 16, and theircontact circuits driving the solenoid valves 8, 11, 14, 20, 21 and 22and the valves (not shown) for closing the circuits of the fuel fed tothe preheaters 9 and 12.

At a normal run of the furnace for the partial combustion, theelectromagnetic contacts and the automatic valves 20, 21 and 22 areclosed and the valves 8, 11 and 14 are open. Oxygen fed through conduit7 and heated to a temperature of about 600 C. in the preheater 9, isintroduced in the mixing zone 1, where it is mixed with the hydrocarbonto be pyrolyzed, fed through conduit and also preheated to about 600 C.in the preheater 9. The gaseous reagents are completely mixed in chamber2 and then, passing through the parallel pipes of the distributor 4,they enter the pyrolysis chamber 5, where they are ignited. The gaseousreaction products are cooled by transversely injecting water from thesprayer 6, whereafter they pass off through conduit 13 to the acetylenepurification and concentration unit.

One example of valves and valve control circuits is showndiagrammatically in FIGURE 2. On each of the inlet lines and on theoutlet line is an emergency shutoff valve: 8 for the oxygen feed line 7,11 for the hydrocarbon feed line 10, 14 for the product gas exit line13, and 26 for the preheater fuel line 25. For quick operation thesevalves are illustrated as sliding gate valves of the guillotine typehaving operating levers, sufficiently weighted at 30 to close the valveimmediately when released, and a magnetic latch mechanism 31 adapted solong as it is energized to hold up the valve and the weight 30 duringnormal operation but instantly to release them when the electromagneticcoil 32 is deenergized.

A supplementary shut-otf device is shown in this example, i.e., thepneumatically operated flow regulator valves 35 and 36, respectively,for the oxygen and methane supply lines. These are shown asspring-operated to closed position and pneumatically operated to openposition, being regulated for normal operation by pneumatic pressurelines with pressure-control devices represented by the squares 37, 38;but, for purposes of this invention, solenoid-operated valves 39, 40 areconnected between the control devices, 37, 38 and the regulator valves35, 36. Normally, these solenoid valves merely connect the pneumaticallyoperated valves 35, 36 through the regulators 37, 38, to the pneumaticpressure lines; but, when the solenoid is operated by an emergencysignal from the temperature-sensing device 16, these valves 39, 40 closethe connections to the regulators, 37, 38 and vent the pressure linefrom the valves 35, 36, so that each valve is closed by action of itscontained spring.

Similar valves 20, 21 and 22 control the emergency supply of asmothering gas such as nitrogen. Valves 5 and 22 are normallypneumatically held closed against the pressure of their springs 41, andare opened by the pressure of the springs when the pneumatic pressure onthe pneumatic diaphragms 41 is vented by operation of valves 44 when themagnetic coils 45 are energized. 6

Valve 21 is inverted, in that it is normally held closed by the springand is opened by pneumatic pressure.

The electrical circuit for emergency closing of the valves connects allthe solenoids 32 and 45 for valves 14, 20, 22, 35, 36, 8, 11 and 26 andthe relay 56 in parallel with each other from the power source 47 and inseries with relay 48 which completes the circuit for all the valves backto the power source 47. Similarly, supervisory alarms will ordinarily beused on the compressed air and smothering gas lines, to be sure thatthey are always ready for emergency operation.

The electrical circuit, as shown, being an emergency protective device,should ordinarily be designed for closed circuit operation with theusual supervisory alarms (not shown) to warn of any failure in thecircuit.

With the circuit thus closed in normal operation, the armatures of thesolenoids 32 are pulled up (as shown), the connected bell cranks beingswung about their fixed pivots 50 so as to push home the latch bolts 31to engage under the catches on the valve stems, as shown. The valvestems are urged down against the latches by the weighted levers 30pivotally mounted at 51.

The solenoid-operated valves 39 and 40 are held in their upper position,as shown, where the upper vent passage is closed and the lower passageconnects the air pressure to the diaphragm chamber 42, so that the airpressure pushes down the diaphragm and the valve stem connected to it.

The same is true of valves 20 and 22, but with the valves 20 and 22pushing down the valve stem closes the valve, whereas the valves 21, 35and 36 are opened when their stems are similarly pushed down. The valve21 is similarly operated, but is energized through a delay relay 55, thedelaying device of which is set to delay closing of the circuitsufiiciently after the temperature limit is reached at 16, so thatpurging of the mixing chamber and furnace begins before additionaloxygen in the pipe 7 is pushed along by the nitrogen admitted at 18.

The opening of relay 48, by action of the temperatureresponsive device16 de-energizes all of the coils 32, and E6. Valves 8, 11, 26, 35, 36and 14 are therefore immediately closed, to isolate the mixing chamberand furnace from the reagent supplies and the product treating systems;valves 22 and 20 are immediately opened to flood the isolated part ofthe apparatus with the smothering gas; and only later, after thepredetermined delay, the valve 21 also operates to blow the smotheringgas into the oxygen feed line when the relay 55 is closed so as toenergize its solenoid 45a and thereby vent its diaphragm chamber 42through valve 44a. After a sufficient delay, to assure extinguishing ofthe fire, the relay 48 is again closed and the system is once morerestored to condition for operation. Only the amount of nitrogen (orother smothering gas) in the pipes and furnace is left in the system. Itis readily separated from the product gases, by renewed normaloperation. While the fire area is isolated between the closed valves 35,36 and 14, any excess pressure is vented through the water trap 15; and,advantageously, the nitrogen or other smothering gas is supplied at apressure sufficient to cause such venting so as to assure purging theapparatus of any burning gas before operation is resumed.

When a backfire or a spontaneous ignition occurs in the mixing chamber2, the temperature suddenly rises, the increase producing substantiallyinstantaneous response by the temperature-responsive device 16, whichautomatically initiates the following simultaneous effects by energizingthe magnetic circuits and under the action of the solenoid valves:

(1) Closing the shut-off valves 8 and 11 feeding the gaseous reagents,said valves being automatic and rapidly working, advantageouslyguillotine valves.

(2) Opening the automatic valve 22, thereby blowing in nitrogen andimmediately purging conduit 10 downstream from the stop valve.

(3) Opening the automatic valve 20, thereby blowing in nitrogen andpurging conduit 7, near the inlet of the mixing chamber, to block theoxygen contained within the conduit 7 from continuing to supportcombustion.

(4) Closing the automatic valve 14 on the outlet conduit 13 of thepyrolysis gases, immediately downstream from the pyrolysis furnace, saidclosing forcing the venting of the gases through the safety device 15.

(5) Closing the heating devices of the preheaters 9 and After apreviously determined period corresponding to that required for purgingall the hydrocarbon circuit downstream the valve 11, plus a margin ofsafety, the automatic valve 21 feeding nitrogen opens, the nitrogen thusintroduced then purging all the oxygen circuit downstream from the valve8.

Under such circumstances, the extinction of the flame produced in themixing chamber 2 is substantially instantaneous in such a manner thatthe detecting thermocouple 16 in the mixing chamber is not damaged.

For controlling the efiiciency of the process of this invention, sometwenty premature ignitions of the hydrocarbon to be pyrolyzed have beencaused in the mixing chamber 2 and it has been observed that:

(1) The bare thermo-couple was not melted and had not been damaged.

(2) The pre-ignition detection by the thermo-couple was substantiallymore rapid than with a pressiometer (connected directly on the mixingchamber and detecting a combustion by the pressure difference betweenthe lower part and the upper part of said chamber), provided as anadditional safety device.

A variety of temperature-responsive devices are already known which arecapable of operating the relay 48 in response to a predetermined hightemperature. We have referred to a thermocouple as a particularlyadvantageous example of such devices, as it is rugged, capable ofrepeated operation and not destroyed by the temperature to which itresponds.

We claim:

1. In the pyrolysis of hydrocarbons by partial combustion, a process forextinguishing undesired pro-ignition flame in a pre-mixing zone adjacenta high-temperature reaction zone in said pyrolysis process continuouslyfed by flammable gas and a flame supporting gas, which comprisesshutting off said pre-mixing and reaction zones from the supplies ofsaid gases fed thereto and from the reacted product gases producedtherein, flooding said zones thus shut off with a smothering gas anddiverting the flow of gases from said zones through a discharge into theatmosphere.

2. A process as defined in claim 1 in which said shutting off of saidzones and said flooding of said smothering gas are automaticallyresponsive to a temperature substantially above normal in saidpre-mixing Zone.

3. A process as defined in claim 1 in which said shutting off of saidzones and said flooding of said smothering gas are effected byelectrically controlled valves and which a thermo-couple in saidpre-mixing zone controls the operation of said valves in response to atemperature substantially above normal therein.

4. A process as defined in claim 1 in which said shutting off occurs onboth upstream and down-stream sides of said zones and beyond the pointsadjacent said zones where said gases are hot.

5. In the pyrolysis of hydrocarbons by partial combustion, a process forrapid extinction of flame within a mixing chamber fed by oxygen andhydrocarbon gas preheated to near the flash point of the hydrocarbon inthe oxygen which comprises shutting oif the oxygen feed stream at aposition upstream of that at which it is heated to said temperature andupstream of that at which it meets the hydrocarbon, blowing nitrogen athigher pressure into the feed stream at a point adajcent to the mixingchamber, whereby oxygen is blocked, replacing the hydrocarbon feed withnitrogen upstream of the means for preheating the hydrocarbon, andventing off flame products and nitrogen downstream from said chamber,whereby nitrogen flows through the mixing chamber.

6. The process according to claim 5 which includes introducing, after ashort delay, nitrogen close to and downstream of the point at which theoxygen feed stream is shut off whereby the oxygen theretofore blocked insaid stream by the higher pressure nitrogen is flushed from said streamthrough the mixing chamber by the resulting flow of nitrogen.

7. The process according to claim 5 in which the outlet for the reactedgases from said pyrolysis is shut off immediately when flame is detectedin the mixing chamber.

8. The process according to claim 5 which further comprises continuallydetecting a temperature in the mixing chamber, and automaticallyinitiating said steps of shutting off feed and blowing in smothering gasin response to abnormal temperature rise resulting from ignition of thegases therein.

9. A process as defined in claim 1 in which said shutting off of thefeed supply of said flame-supporting gas occurs at a substantialdistance upstream from said zones, and in which said smothering gas isblown into said feed supply stream first closely adjacent said zoneseffecting immediate smothering of said pre-ignition flame in saidpro-mixing zone by depriving said flame of further flame-supporting gasand then, after a delay suflicient to smother and extinguish said flame,additional smothering gas is blown into said flame-supporting gas feedstream at a point closer to said shut-off point for purging said feedstream.

References Cited in the file of this patent UNITED STATES PATENTS2,155,119 Ebner Apr. 18, 1939 2,247,181 Berhoudar June 24, 19412,590,436 Luten Mar. 25, 1952 2,784,068 Beggs et al Mar. 5, 19572,818,326 Eastman et al Dec. 31, 1957 2,838,585 Lehrer June 10, 1958

1. IN THE PYROLYSIS OF HYDROCARBONS BY PARTIAL COMBUSION, A PROCESS FOREXTINGUISHING UNDESIRED PRE-IGNITION FLAME IN A PRE-MIXING ZONE ADJACENTA HIGH-TEMPERATURE REACTION ZONE IN SAID PYROLYSIS PROCESS CONTINUOUSLYFED BY FLAMMABLE GAS AND A FLAME SUPPORTING GAS, WHICH COMPRISESSHUTTING OFF SAID PRE-MIXING AND REACTION ZONES FROM THE SUPPLIES OFSAID GASES FED THERETO AND FROM THE REACTED PRODUCT GASES PRODUCEDTHEREIN, FLOODING SAID ZONES THUS SHUT OFF WITH A SMOTHERING GAS ANDDIVERTING THE FLOW OF